services.AddScoped<YourDbContext>(svc =>
     {
         var connString = ... logic to get the conn string with the right password from HashiCorp vault;
         var dbContextOptions = new DbContextOptionsBuilder<YourDbContext>();
         dbContextOptions.UseSqlServer(connString); //Or w/e ef provider for db you use
         return new YourDbContext(dbContextOptions.Options);
     });